Cardiac arrhythmia, such as atrial fibrillation, occurs when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. Important sources of undesired signals are located in the tissue region, for example, one of the atria or one of the ventricles. Regardless of the sources, unwanted signals are conducted elsewhere through heart tissue where they can initiate or continue arrhythmia.
Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. More recently, it has been found that by mapping the electrical properties of the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy, it is possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions.
In this two-step procedure—mapping followed by ablation—electrical activity at points in the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the target areas at which ablation is to be performed.
For greater mapping resolution, it is desirable for a mapping catheter to provide very high density signal maps through the use of a multitude of electrodes sensing electrical activity within a small area, for example, about a square centimeter. For mapping within an atria or a ventricle (for example, an apex of a ventricle), it is desirable for an electrode assembly to collect larger amounts of data signals within shorter time spans. It is also desirable for such an electrode assembly to be adaptable to different tissue surfaces, for example, flat, curved, irregular or nonplanar surface tissue, yet remain in a predetermined configuration where electrode spatial relationships are generally maintained during sensing and mapping. With more complex electrode geometries, it is further desirable that the electrode assembly be readily collapsible to be advanced through a guiding sheath.